[FR] GraphQL: cases

[c8y3]

Enrich the graphQL API with queries and mutations that allow the manipulation of cases:

• add query case to retrieve an case by its identifier
• add query cases to retrieve a filtered list of cases
• add mutation caseCreate to create a case
• add mutation caseDelete to delete a case
• add mutation caseUpdate to update a case

For the required/optional fields of mutations, mimic the existing REST API (https://docs.dfir-iris.org/latest/_static/iris_api_reference_v2.0.4.html):

• /manage/cases/add for mutation caseCreate
• /manage/cases/update/{case_id} for mutation caseUpdate
• /manage/cases/delete/{case_id} for mutation caseDelete

For query cases, the filters available in section overview should first be implemented. Then see whether the remaining fields can be filtered as well. The return type should be a paginated list (decide whether to follow the relay standard for the pagination results or not)

Do not forget to handle permissions correctly.